A known antijackknifing device has gained wide acceptance in the practice.
In the device, hydraulic power cylinders limit the jackknifing angle when it exceeds the value related to a given steering angle. A signal device sensing the turn of the steered front wheel, and a signal device sensing the jackknifing angle of the two vehicle units are connected to a programmed electronic unit, the electric signal given by them is compared with the jackknifing angle related to the steering angle fed into the electronic computer unit in advance, and depending on the evaluation, the hydraulic valve or at least one of the working spaces is closed. The device does not influence the jackknifing angle and the running characteristics of the motor vehicle until the jackknifing angle does exceed the programmed value related to the steering angle, when it comes into action steplessly to prevent the increase of the jackknifing angle, or its variation in one of the directions. The device offers protection against jackknifing of the vehicle, which is dangerous, especially in the case of driven trailers, or against drifting caused by the centrifugal force arising when the trailer travels in a curve.
In a further antijackknifing solution, a signal device is built in, sensing the turning direction of the steering spindle, the output signal of which is in functional connection with the valves arranged in the line that connects the hydraulic working space with the hydraulic fluid reservoir.
In the neutral position of the steering spindle, the outlet lines of both working spaces are closed, the pistons of the working spaces preventing variation of the angle between the towing vehicle and trailer. When turning the steering spindle, the valve that shuts the working space, which in a closed position prevents variation of the jackknifing angle related to the steering direction, opens, thereby freeing the jackknifing angle variation in this direction.